Antennas are well-known for communication and radar systems. Antennas act as a transducer between electromagnetic wave propagation in free space and guided electromagnetic wave propagation in transmission lines. It is possible to design antennas to concentrate the radiated electromagnetic energy in a principal direction and conversely receive electromagnetic energy from a principal direction.
The ability of an antenna to concentrate the transmitted energy in a particular direction is commonly known as directivity or gain. It is common to speak of gain as a function of angle or direction which leads to a so-called radiation pattern for a given antenna. The radiation pattern will typically comprise a main beam within which the majority of the electromagnetic energy is concentrated and a plurality of side lobes or minor beams which diminish in energy as the angular separation from the main beam increase.
The far-field radiation pattern, namely the radiation pattern far from the antenna where the wavefronts are substantially planar (and the E and H-field of the electromagnetic field are in phase) is a key design specification when creating an antenna. It is found that a highly directive antenna is usually bulky, heavy and often expensive. In situations where it is required to steer a beam, then phased antenna arrays are often employed, however scanning range is often angularly limited to avoid significant side lobes developing in the radiation pattern. Therefore, it is desirable to tailor a far-field radiation pattern for a given antenna.